The Biomechanics of Bruising Heather Black1, Sylvie Coupaud1, Niamh NicDaeid2, Philip Riches1 1Department of Biomedical Engineering, University of Strathclyde, Glasgow 2Centre for Anatomy and Human Identification, University of Dundee, Dundee ([email protected]) Methods Introduction Haemoglobin concentration[1], photographic[2] and colour pattern identification[2,3] have been used for characterising contusions. However, few studies specifically focus on the mechanics of bruise formation[2,4]. Ultimately, we wish to determine if there is a link between the time progression of bruising and mechanics of impact, which necessitates controlled impact generation. Several studies have used a paintball marker[3, 5-7], yet to date their suitability has yet to be assessed. Therefore, this study aimed to determine if a BT-4 Combat marker is suitable for generating controlled blunt impacts. A fully pressurised marker (~3000 psi), was secured via a table mount and reusable paintballs (mass of 2.6 g) were fired through a chronograph (Figure 1), until the cylinder depressurised. This procedure was repeated a further 5 times to determine the repeatability of firing velocity. To determine accuracy, carbon paper targets were placed at distances of 4, 5, 6, 7 and 8 m and 40 shots were fired at each. Figure 1. Experimental set-up of the marker and chronograph Results and discussion Above 800 psi the marker velocity is effectively constant, whilst below this value, velocity decreases with pressure (Figure 2). There was no significant difference between the 6 tests and above 1500 psi, the average velocity was 71.27 ± 0.529 ms-1. 3000 2500 Approx. Pressure (psi) 2000 1500 1000 500 0 90 80 Velocity (mps) 70 60 Figure 3. Examples of impact overlap and increasing dispersion at 4 and 6 m Test 2 50 Test 3 40 Test 4 30 Test 5 20 Test 6 0 10 0 0 100 200 300 Shot No. 400 500 600 Distance (m) x sd (cm) y sd (cm) 4 1.45 1.87 5 1.79 2.15 6 2.77 2.72 7 2.31 3.74 8 2.15 2.28 Average 2.09 2.55 Table 1. x and y standard deviations around the mean impact location Conclusions 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 -24 -26 -28 -30 -32 -34 2 4 Distance (cm) 6 8 10 12 14 16 18 8m 7m 6m 5m 4m Laser Figure 4. Average impact location ± x and y standard deviations for each target distance References [1] Impact velocity and location were highly predictable. Thus the paintball marker is appropriate for use as a controllable, repeatable and reliable method for blunt impact generation. Combined with imaging techniques such as infrared and cross polarisation photography, this will allow for both the mechanics of impact and the aging of bruise injuries to be investigated. Distance (cm) Figure 2. Firing velocities for all 6 tests From 200 shots, the impact location of 177 were successfully recorded with impact overlap resulting in lost data (Figure 3). Marker trajectory and laser sight were divergent (Figure 4) resulting in predictable vertical (~2cm/m) and horizontal (~1 cm/m) error. The effect of gravity on marker impact location was not apparent. Impact dispersion increased with distance (Figure 3, Table 1). 6m 4m Test 1 [2] [3] [4] [5] [6] [7] Randeberg LL, Larsen ELP, Svaasand LO. Characterization of vascular structures and skin bruises using hyperspectral imaging, image analysis and diffusion theory. J Biophotonics 2010;3:53–65. Black HI. The biomechanics of bruising. University of Strathclyde, 2013. Scafide KRN, Sheridan DJ, Campbell J, Deleon VB, Hayat MJ. Evaluating change in bruise colorimetry and the effect of subject characteristics over time. Forensic Sci Med Pathol 2013;9:367–76. Desmoulin GT, Anderson GS. Method to investigate contusion mechanics in living humans. J Forensic Biomech 2011;2:1–10. do Randeberg LL, Baarstad I, Løke T, Kaspersen P, Svaasand LO. Hyperspectral imaging of bruised skin. Proc SPIE 2006;6078:1–11. Randeberg LL, Skallerud B, Langlois NEI, Haugen OA, Svaasand LO. The optics of bruising. In: Welch AJ, Gemert MJC, editors. Opt. Response Laser-Irradiated Tissue, Dordrecht: Springer Netherlands; [7]2011, p. 825–58. Randeberg LL, Hernandez-Palacios J. Hypserspectral imaging of bruises in the SWIR spectral region. Proc SPIE Photonic Ther Diagnostics VIII 2012;8207:1–10.
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